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1.  Skeletal effects of parathyroid hormone (1–34) in ovariectomized rats with or without concurrent administration of salmon calcitonin 
AAPS PharmSci  2001;3(4):19-25.
This study evaluated the effect of parathyroid hormone (PTH) infusion alone or in combination with salmon calcitonin (sCT) in ovariectomized (OVX) rats and compared it with daily PTH injections alone or in combination with sCT infusion. Female Sprague-Dawley rats were divided randomly into 6 groups and were either bilaterally ovariectomized or underwent a sham operation; they were then treated for 4 weeks, beginning the day after surgery. Each group of OVX rats received either PTH infusion (group 1), PTH+sCT infusion (group 2), sCT infusion+daily PTH injection (group 3), or daily PTH injection (group 4). One group each of OVX (group 5) and sham-operated rats (group 6) received daily injections of vehicle alone. PTH was injected at 80 μg/kg/day and infused at 40 μg/kg/day, whereas sCT was infused at 10 μg/kg/day. The animals were sacrificed 28 days after treatment, and cancellous bone volume was measured in the tibial metaphysis. Similar to daily PTH injections, continuous infusion of PTH alone increased cancellous bone volume significantly over that seen in vehicle-treated OVX and sham-operated rats. Although cancellous bone volume after continuous infusion of PTH+sCT was also significantly higher than that seen in vehicle-treated OVX and sham-operated rats, the increase was significantly lower than with the other 3 nonvehicle treatments. The increase in cancellous bone volume after administration of sCT infusion along with daily PTH injections was not different from that with daily PTH injections alone. Thus, at the doses tested, the beneficial effects of PTH injection were not apparently improved by PTH infusion or by combination with sCT.
doi:10.1208/ps030427
PMCID: PMC2751216  PMID: 12049490
Salmon calcitonin; human parathyroid hormone (1–34); infusion; ovariectomized rats; cancellous bone volume
2.  A short-term (accelerated release) approach to evaluate peptide release from PLGA depot formulations 
AAPS PharmSci  1999;1(3):1-6.
An accelerated method to evaluate peptide release from poly(dl-lactide-co-glycolide) (PLGA) depot formulations in short time is described. Peptide-loaded microspheres were made from hydrophilic 50∶50 PLGA by a dispersionsolyent extraction technique, and peptide release was studied at 37°C and at higher temperatures in various media. For all accelerated conditions, release was faster at temperatures above the glass transition, Tg, of the host polymer. Complete release of peptide from 8600 MW PLGA was achieved in 35 hours at 50°C in buffered and nonbuffered media containing 0.5% polyvinyl alcohol (PVA). Type of release media and concentration of PVA influenced the release profiles. A PVA concentration of 0.1 to 0.5% was found to prevent aggregation of microspheres at higher temperatures, with an increase in release at the higher PVA concentration. Peptide release was associated with a reduction of pH of the releasing media and increased mass loss. Complete peptide release at pH 4 from 8.6 kd and 28 kd PLGA at 50 and 60°C occurred within 30–40 hours and correlated well with the real-time release at 37°C and pH 7.0. At the higher molecular weight, a slightly longer accelerated release time and higher temperature were required to correlate with the real-time release. The data suggest that by optimization of release conditions such as temperature, surfactant concentration, buffer component, and pH, an accelerated study could be employed to evaluate depot formulations for a given polymer type.
doi:10.1208/ps010307
PMCID: PMC2761121  PMID: 11741203
peptide loaded microspheres; depot formulation; accelerated release; elevated temperature; PLGA

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